Fungal growth is a serious threat to human health, and the potential costs for remediation or replacement of contaminated building materials are astronomical. Fungal spores, released from surface growth, are well-recognized as allergens, and additional concerns have been raised due to toxic byproducts of at least one species. According to recent studies by Gorny et al. (Appl. Environ. Microbiol., July 2002, p. 3522-3531), occupant exposure to various health problems, including those referred to as “sick building syndrome,” is increasing. Further concern is being raised by human allergic responses, similar to that observed with fungal spores, to fungal fragments that can be released at much lower humidity levels (as low as 20%).
Paper and paperboard used in those building materials have been observed as the sites for such fungal growth. Typical moisture in paper, paperboard, and building materials is sufficient to maintain growth. The cellulose of the paper and paperboard, along with the residual contaminants within the fiber web, offer a sufficient food source that is enhanced by other building product components such as starch binders.
Since fungi can grow in temperatures from as low as 40° F. to as high as 130° F., most indoor conditions, as well as a large segments of outdoor conditions, will easily allow their growth. Although efforts have been made to use careful construction practices and humidity control to limit fungal growth, fungi contamination problems have been observed in regions such as the Northeast U.S. where relative humidity rarely exceeds recommended maximums, and building materials were not exposed to the weather. Atmospheric fungal spores provide sufficient inoculation of fungi to the materials, and added moisture from condensation or water damage makes the threat of fungal contamination more likely.
Homeowners typically see fungal growth in closets, along baseboards and on bathroom walls; removal of installed panels may reveal hidden growth on the backside. Areas with even minor water damage or condensation are often heavily contaminated. Growth is visible as dark green or black spots that can grow to a complete covering of the affected area. Many after-market treatments, usually based on chlorine bleach, lighten the spots. Such treatments tend to damage the paint or coating after multiple treatments and do not prevent return of fungi.
Gypsum panels are used for drywall building products and are in heavy use for residential, educational, and commercial buildings. Gypsum panels are used primarily for interior wall and ceiling construction, and some specialty panels are used in exterior applications. Even though fungal contamination can come from the gypsum core, made of calcium sulfate hemihydrates, the primary location for fungal growth on gypsum panels is the facing paper that covers each side of the gypsum core. Once installed, gypsum panels can make treatment and/or remediation extremely difficult and expensive, as fungal contamination may be enclosed and inaccessible.
Current methods used to render gypsum board mold-resistant per industry metrics generally require the use of high levels of antimicrobial agents in the cellulose-based facing paper. Also, fixatives, such as cationic fixatives, are generally needed to enhance the efficacy of the antimicrobial when it is added to the wet-end of the paper-making process. In addition, antimicrobials sometimes also need to be added to the gypsum core to further enhance mold-resistance. The use of high antimicrobial loadings in gypsum board is commercially undesirable for a number of reasons, cost being the primary consideration. In addition, production difficulties often arise when attempting to use high levels of antimicrobials.
Thiabendazole, zinc pyrithione, and diiodomethyltolylsulfone (DIMTS) have been applied commercially in mold-resistant paper facers for use in gypsum board. Thiabendazole (TBZ) and zinc pyrithione (ZPT) have been replaced predominately by DIMTS and the technology described in US20060169431A1, which is incorporated herein by reference. Commercially practiced loadings for DIMTS-treated paper used for gypsum wallboard are generally on the order of 700-1000 ppm. Sodium pyrithione, a highly water-soluble antimicrobial, is sometimes used to treat the gypsum core of mold-resistant wallboard.
A continuing need exists for wallboard materials that provide enhanced mold resistance and that require lower biocide loadings.